Friday, April 18, 2008

Fan-assisted trucks

Travel at 70 mph on a motorway, and approximately 65 per cent of the fuel you burn goes to overcoming aerodynamic drag. So even a slight reduction in drag will significantly improve fuel consumption. This is a particular problem for lorries and buses.

Kambiz Salari at the Lawrence Livermore National Laboratory in California, US, and colleagues say that much of the drag from a "bluff body" such as bus or truck comes from the air vortices generated behind the vehicle as it moves. So instead of making these vehicles more wedge-shaped, significant fuel economies can be made by modifying their behind.

Salari has designed a set of fans to be fitted to the back of a cab or trailer that inject air into the air flow in a way that significantly reduces the turbulence it generates. This should in turn improve fuel economy, although the patent does not say the scale of the potential gains.

Giant fans on the back of a vehicle will rob the engine of power, and take up space and weight, probably producing a net LOSS of mileage.

What about low-drag aerodynamic modifications? In the US, many truck cabs have an extra extension that bridges most of the gap between the cab and the trailer, reducing wind friction and improving mileage over 10% at minimal cost. Smooth tarps stretched over irregular loads can make further improvements, but few do this, except to secure loads.

Cars could have transparent plastic extensions (that double as extra impact bumpers) on the front or rears to make them aerodynamic, approximating a low-drag ellipsoid.

Would not the trailer part reduce drag if a 'spoiler' was attached to all rigs. Could even be part of the actual design of all trailers by a slight modification to lower the roof line at the back. It has been part of aerodynamics for 50 years or more